Object Oriented Design

Write Python code that’s easier to change, test, and extend.

You already know how to write classes. Now learn how to decide what belongs in them, how they should collaborate, and how to handle changing requirements.

Object Oriented Design walks you through 15 guided exercises that connect everyday Python features with practical design decisions. You’ll work through focused problems, then bring the pieces together in Lighthouse Trail, an extensible board game engine for two to four players.

• Choose between composition and inheritance, and give each object a clear responsibility.
• Build useful interfaces with properties, alternative constructors, abstract classes, and small mixins.
• Apply Strategy, Factory, and Observer to replace behavior, create objects, and communicate changes.
• Model state transitions and use Command to support history, undo, and redo.
• Connect existing code through adapters and make dependencies explicit with manual dependency injection.
• Use SOLID principles to refactor a class that has taken on too much work.

Each exercise starts with a concrete problem and a design before the code. Guided implementation, explanations, tests, edge cases, common mistakes, and an extension challenge help you understand why the solution works.

In the final project, you’ll combine turn management, interchangeable scoring rules, event notifications, and move undo into a working game engine. The book also includes solutions, further extensions, a glossary, and references to the official Python documentation.

Designed for readers comfortable with functions, collections, control flow, and basic classes, this book uses Python 3.12 or later and the standard library. It is Book 2 in Intermediate Python in Practice and can be studied on its own.